1. Field of the Invention
This invention relates to a clutch mechanism through which a machine may be driven, and more particularly, to such a mechanism which will disengage upon occurrence of an overload in the driven machine, the clutch mechanism including means for varying its torque output during operation.
2. Description of the Prior Art
Overload clutches are known which are capable of disengaging upon the occurrence in the driven machine of an overload requiring a clutch torque output which exceeds a predetermined value, as disclosed in U.S. Pat. Nos. 2,781,118 and 3,132,730, for example. However, as far as we are aware, such known clutches offer inadequate protection in respect of a great number of commercial applications wherein the driven machine has a high starting inertia but a relatively low running torque since the clutch must be able to accommodate the starting inertia, thus establishing the maximum torque value at which the clutch will respond in the event of an overload. Thus, if during running at low torque an overload occurs in the driven machine which does not reach the level of the starting inertia, the clutch will not disengage, thereby offering no protection for that condition.
An additional disadvantage of known overload clutches is their inability to accommodate conditions wherein the driven machine develops different torque levels during its running cycle. Thus, in some instances, while normal running generally is at relatively low torque, temporary high torque levels will occur as part of the normal running cycle, and such temporary high torque levels may cause known overload clutches to disengage, thus undesirably interrupting the normal operation cycle.
Additionally, when the driven machine is intentionally shut down by shutting down the prime mover, the inertia in the driven machine causes a high torque to be applied to the clutch. In this condition, disengagement will occur if that torque exceeds the torque for which the clutch is set; but continued engagement under this condition is desired so that the prime mover, clutch and driven machine will be set for start-up for the next operational cycle.
Those persons skilled in the art will appreciate the need for a clutch of the class described which can (1) accommodate high starting inertia; (2) respond to an overload at low running torque; (3) adjust its output torque during operation of the driven machine to accommodate normal running torque variations while at all times providing rapid overload protection; and (4) accommodate stopping torque without disengaging.
We have actually constructed a successfully operating and commercially desirable overload clutch based upon those requirements.